Are you older enough for tattoos?
That helped me through my SI issues. I know it sounds stupid but I like tattoos, seeing and getting them. You have to be 16 with parents persmission and 18 to do it on your own. When I got a strong urge I would schedule a tattoo and wait for it. Just scheduling it, even if I had to wait a week, made it better.

Sorry if this reply is stupid, just trying to share what has worked for me. I don't get tattoos that often anymore and I don't have the SI urge either. Because I know there is a solution when I need it. That helps keep it away for me.